This invention relates to printed circuit boards in general and more particularly to a method of fabricating a foldable printed circuit board.
Printed circuit boards which are folded have long been known in the art and essentially provide a means for minimizing space requirement in electronic packages or housings which employ printed circuit wiring. The prior art is replete with a number of patents which are directed to foldable printed circuit boards.
According to such prior art techniques, these boards have been built with multiple rigid board sections which are bonded to flexible tape circuitry. Manufacturing of such assemblies is expensive because the assemblies require special support fixtures and other devices to enable them to be properly fabricated. The prior art is cognizant of such problems and there have been many attempts to provide folded boards in order to conserve space and to enable electronic components mounted on such printed circuit boards to be placed in housings having a fixed service area.
For examples of such suitable prior art, reference is made to U.S. Pat. No. 3,716,846, issued on Feb. 13, 1973 and entitled CONNECTOR SHEET WITH CONTACTS ON OPPOSITE SIDES by P. Volckart, et al. This patent basically shows a connector sheet or band with a printed circuit only on the front surface. The sheet has a marginal portion bent along a fold line upon the rear surface. Input and output connectors extended across the fold line and are arranged symmetrically and form registering electrically connected contact portions in the front and the rear of the connector sheet.
As one can ascertain by reference to the above-noted patent, in order to make the contact and permit folding of the board, the reference employs conductor strips which are extremely thin devices. The problem with such strips is that if the board is folded and reopened and folded again, the strips break and are damaged due to such multiple folding and unfolding operations. Hence these boards are relatively fragile and are not meant for rugged operation.
Apart from these factors is that the board based on the conductor strips utilized to implement the fold enable very low current levels to be carried by the conductor strips thereby adversely affecting the boards in regard to biasing voltage supplies, ground returns and so on.
U.S. Pat. No. 3,971,127 issued on July 27, 1976 to W. J. Giguere and is entitled A METHOD OF FABRICATING A PRINTED WIRING BOARD ASSEMBLY. This patent again describes a method of fabricating a folded printed wire board assembly which includes cutting an aperture into a rigid board and bonding a flexible circuit tape to one side of a board so that the tape bridges the aperture.
Essentially, in regard to this patent, this is very similar to prior art techniques where the connectors across the aperture are circuit tape and hence the circuit tape employed is very fragile and does not enable one to constantly open and close the board nor does the circuit tape provide a mechanical bonding assembly for one side of the board to the other. These are various other patents which show various other techniques providing folded board assemblies as for example U.S. Pat. No. 3,819,989, issued on June 25, 1974 entitled PRINTED WIRING BOARD ASSEMBLY to D. P. Braune which shows a printed wiring circuit board assembly fabricated from a single blank flexible tape carrying a plurality of conductors extending to circuitry carried by the circuit boards. In this patent the boards are arranged at right angles to a main tape at the end of tape tabs carrying branching conductors to board circuitry. Tape tabs are then folded and refolded so that the boards come to rest in mutually parallel planes perpendicular to the main tape.
Other patents such as U.S. Pat. No. 4,066,851 and U.S. Pat. No. 4,149,219 as well as U.S. Pat. No. 4,216,523 relate to various techniques showing printed circuit boards employing fold lines or other conductors to enable folding of the board to conserve space in subsequent housing assemblies.
In any event, as one can ascertain from the above prior art, most of the techniques employing foldable boards used circuit tape or other very thin flexible conductors in order to enable folding of the board. The prior art techniques were difficult to implement and resulted in relatively fragile assemblies with permitted folding but did not permit easy access or did not permit the continuous folding and unfolding of the board. Furthermore, the conductors employed were difficult to fabricate as well as the fact that the boards were difficult to fabricate, and due to the nature of the circuit tapes, these circuits were not capable of carrying high current and did not provide any mechanical support to the folded assembly.
It is of course apparent that printed circuit boards which are employed in commercial products require the necessity to implement repairs on such boards and essentially test and repair such boards by the continuous folding and unfolding of the boards. This of course requires very rigid conductors connecting the boards together and furthermore which conductors would provide both mechanical and electrical connections for the board. It is also apparent that one needs to fabricate such boards as rapidly as possible using high speed equipment in order to produce a great number of boards with a minimum of time and operations.
It is therefore an object of the present invention to provide an improved printed circuit board which is capable of being folded which can be manufactured inexpensively and accurately.
It is a further object to provide a foldable printed circuit board which is extremely rugged while providing good electrical contact between the folded halves and further enabling the continuous folding and unfolding of the board for test purposes.
It is a further object to provide a foldable printed circuit board which can be fabricated utilizing conventional high speed techniques for printed board fabrication such as for use with automatic insertion machines which allows components to be rapidly placed on a printed circuit board.